Disk array device, method for controlling the disk array device and storage system

ABSTRACT

A disk array device is equipped with a plurality of input/output channels that receive data input/output requests from an external device, a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels, a disk drive device, a disk control module that performs data input/output to and from the disk drive device, and a communication module that communicatively connects the input/output channels with the disk control module. The disk array device also includes a consistency maintaining module that can perform a consistency maintaining processing to maintain consistency of data stored in each of the cache memories. According to the content of the data input/output request received from the external device, an execution order of a response processing to respond to the external device according to the data input/output request and the consistency maintaining processing is controlled.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a disk array device, a control methodfor the disk array device, and a storage system.

2. Related Background Art

A common disk array device has a structure in which a disk adapter thatcontrols input/output of data to disk drives, an input/output channelthat controls connection with a host computer, and a cache memory areconnected to one another via a network switch provided inside the diskarray device.

As a result, the input/output channel, the disk adapter and the cachememory compete for traffic within the network switch of the disk arraydevice, which increases the usage rate of the network switch, which inturn reduces the response speed to the host computer.

The present invention was conceived in view of the situation, andrelates to a disk array device, a control method for the disk arraydevice, and a storage system.

A disk array device in accordance with an embodiment of the presentinvention includes: a plurality of input/output channels that receivedata input/output requests from external devices; a plurality of cachememories, each of which is provided for each of the input/outputchannels and connected to each of the corresponding input/outputchannels; disk drives; a disk control module that performs datainput/output to and from the disk drives; and a communication modulethat communicatively connects the input/output channels with the diskcontrol module.

Other features of the present invention shall become apparent from thedescription of the present specification and attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows the configuration of a storage system inaccordance with an embodiment example of the present invention.

FIG. 2 is a diagram of the configuration of an input/output channel inaccordance with an embodiment example of the present invention.

FIG. 3 is a diagram of the configuration of a disk adapter in accordancewith an embodiment example of the present invention.

FIG. 4 is a diagram of the configuration of a cache memory in accordancewith an embodiment example of the present invention.

FIG. 5 is diagram of the configuration of a cache memory in accordancewith an embodiment example of the present invention.

FIG. 6 is a diagram of a data table format in accordance with anembodiment example of the present invention.

FIG. 7 is a diagram of a data table format in accordance with anembodiment example of the present invention.

FIG. 8 is a diagram of a command format of an invalidation command inaccordance with an embodiment example of the present invention.

FIG. 9 is a diagram of a command format of an update command inaccordance with an embodiment example of the present invention.

FIG. 10 is a diagram of the data format of a data input/output requestin accordance with an embodiment example of the present invention.

FIG. 11 is a flowchart illustrating a processing that takes place in adisk array device when a data request is received in accordance with anembodiment example of the present invention.

FIG. 12 is a flowchart illustrating a processing that takes place in adisk array device when a data write request is received in accordancewith an embodiment example of the present invention.

FIG. 13 is a flowchart illustrating a processing that takes place in adisk array device when a data write request is received in accordancewith an embodiment example of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

<Overview of Storage System>

FIG. 1 shows an overview of a storage system including a disk arraydevice 1 configured in accordance with an embodiment of the presentinvention. The storage system shown in FIG. 1 is provided with aplurality of input/output channels 10 a–10 d and a plurality of cachememories 11 a–11 d, wherein each of the cache memories 10 a–10 d isprovided for each of the corresponding input/output channels 11 a–11 d.According to this configuration, if data that is the subject of a datainput/output request from a host computer is in one of the cachememories 11 a–11 d provided to correspond to one of the input/outputchannels 10 a–10 d that received the data input/output request, the datacan be sent to the host computer. Consequently, when data is in one ofthe cache memories 11 a–11 d, a response can be sent back quickly to thehost computer.

According to the configuration in FIG. 1, if, for example, datainput/output requests received by different input/output channels amongthe input/output channels 10 a–10 d result in accesses to the same datastored in a storage region of a disk drive, the data that is stored inthe storage region of the disk drive would simultaneously be stored in aplurality of cache memories 11 a–11 d.

In this state, if an update were to take place, for example, on the dataas a result of a new data input/output request received by one of theinput/output channels 10 a–10 d, a processing to maintain consistency ofdata stored in each of the cache memories 11 a–11 d, such as aprocessing to invalidate the data stored in one or more of the othercache memories 11 a–11 d or a processing to rewrite the data stored inone or more of the other cache memories 11 a–11 d, must be performed.

However, in the processing to maintain consistency, communications forinvalidating and communications to notify updated data to the cachememories 11 a–11 d cause an increase in the network switch traffic,which reduces the response speed to the host computer; this would dilutethe effect that can be obtained by providing the cache memories 11 a–11d for the corresponding input/output channels 10 a–10 d.

The processing to maintain consistency, however, is not necessarilyrequired to be immediate or strictly maintained in all cases. Forexample, such processing would not be required when access to datastored in a certain storage region can be made only through a specificchannel among the input/output channels 10 a–10 d.

Further, when accesses from a plurality of input/output channels 10 a–10d are anticipated for the same data stored in one storage region,consistency may not necessarily have to be maintained due to thespecification or nature of software operating on the host computer, oreven if it does, strict consistency may not be required.

In view of the above, in one embodiment of the present invention, a diskarray device may include a plurality of input/output channels thatreceive data input/output requests from external devices; a plurality ofcache memories, each of which is provided for each of the input/outputchannels and connected to each of the corresponding input/outputchannels; disk drives; a disk control module that perform datainput/output to and from the disk drives; a communication module thatcommunicatively connect the input/output channels with the disk controlmodule; and a module to execute a consistency maintaining processing tomaintain consistency of data stored in each of the cache memories. Thedisk array device further includes a module that controls, when a datainput/output request is received, according to the contents of the datainput/output request, the execution order of a response processing to ahost computer for the data input/output request and the consistencymaintaining processing.

When updating data stored in any of the cache memories, the consistencymaintaining processing may take place. The consistency maintainingprocessing includes, for example, a processing to invalidate the samepre-updated data stored in other ones of the cache memories that isstored in the same storage region as the storage region of the diskdrive where the data to be updated is stored; or a processing to updatethe data in the cache memory, as well as the same pre-updated datastored in another cache memory that is stored in the same storage regionas the storage region of the disk drive where the data to be updated isstored.

As described above, a processing to maintain consistency is notnecessarily required due to the specification or nature of softwareoperating on the host computer, or even if it does, strict consistencymay not be required. By controlling the execution order of a responseprocessing to the host computer for an input/output request and aconsistency maintaining processing according to the contents of the datainput/output request sent from the host computer, and by controlling theorder of execution depending on whether consistency must be maintainedor not, the disk array device can be used efficiently. Specifically,when a processing to maintain consistency is not necessarily required, aresponse to the host computer can be made quickly by executing anconsistency maintaining processing after performing a responseprocessing to the host computer.

Furthermore, when there is a plurality of logical volumes, which arelogical storage regions, in storage regions of disk drives and when anidentifier of a logical volume that is the subject of processing for adata input/output request is set in the data input/output request,controlling the execution order can be performed according to thelogical volume identifier set in the data input/output request.

By being able to control the execution order based on the logical volumeidentifier, more variations in setting methods become available; forexample, when individual logical volumes are allocated for eachapplication operating on a host computer, the control of the executionorder can be set easily based on the nature of the application programs.

In another embodiment of the present invention, when a disk array deviceis connected to another disk array device, and the former disk arraydevice receives a data write request as a data input/output request froman external device, the disk array device writes the data designated inthe request to its own disk drives and at the same time sends the writerequest to the other disk array device; when an input/output channel ofthe former disk array device receives the data write request, theinput/output channel operates in either an operation mode to write datato the disk array device's own disk drives (i.e., a normal mode) or anoperation mode to send the write request to the other disk array (i.e.,a copy mode); the execution order is controlled depending on whichoperation mode the input/output channel that received the datainput/output request from the external device is operating.

In this instance, if a processing for a data input/output requestreceived by an input/output channel operating in the copy mode has lessneed for consistency maintenance compared to a processing for a datainput/output request received by an input/output channel operating inthe normal mode, for example, a response to a host computer can be madequickly by executing an consistency maintaining processing afterperforming a response processing to the host computer in the copy mode.

<System Configuration>

The configuration of the storage system in FIG. 1 is described below ingreater detail. The disk array device 1 is connected to host computers,which are external devices, via a communication means such as SAN(Storage Area Network) or LAN (Local Area Network). The disk arraydevice 1 comprises the four input/output channels 10 a–10 d thatcommunicate with the host computers, the cache memories 11 a–11 dprovided for and connected to the corresponding input/output channels 10a–10 d, disk drives 14 a–14 d, four disk adapters 13 a–13 d that areconnected to the respective disk drives 14 a–14 d and controlinput/output of data to and from the respective disk drives 14 a–14 d;and two network switches 12 a and 12 b that connect the input/outputchannels 10 a–10 d with the disk adapters 13 a–13 d.

In FIG. 1, the network switches 12 a and 12 b are provided in plurality,such that there is redundancy in the route between the input/outputchannels 10 a–10 d and the disk adapters 13 a–13 d. However, only onenetwork switch may be provided instead of two. The four input/outputchannels 10 a–10 d receive data input/output requests such as datarequests and data write requests from the host computer. Based on thedata input/output request received by the input/output channel 10 a–10d, the disk array device 1 reads or writes data to or from the diskdrives 14 a–4 d and sends, as necessary, the results or data read to theappropriate host computer.

<Input/Output Channels>

FIG. 2 is an example of the configuration of the input/output channels10 a–10 d. Each of the input/output channels 10 a–10 d has a processor201. Each of the input/output channels 10 a–10 d also has a local memory202 that stores control programs executed by the processor 201 andinformation (data) required for processing. In addition, each of theinput/output channels 10 a–10 d has a host I/F circuit 204 forconnecting with the host computer, as well as network connectioncircuits 203 a and 203 b for connecting with the network switches 12 aand 12 b.

All of these elements are connected to each other by a processor bus205, which is a high-speed signal line bus. The corresponding cachememory among the cache memories 11 a–11 d is also connected to theprocessor bus 205. Through this configuration, the processor 201 is ableto read and write at high-speed to and from the corresponding cachememory among the cache memories 11 a–11 d.

In FIG. 2, the processing in the input/output channels 10 a–10 d isassumed to be performed by having the corresponding processor 201execute the control programs stored in the corresponding local memory202. However, a part or all of the functions of the control program canalternatively be implemented by hardware.

<Disk Adapters>

FIG. 3 is an example of the configuration of the disk adapters 13 a˜13d. Each of the disk adapters 13 a–13 d has a processor 301. Each of thedisk adapters 13 a–13 d also has a local memory 302 that stores controlprograms executed by the processor 301 and information (data) requiredfor processing.

In addition, each of the disk adapters 13 a–13 d has a disk drive I/Fcircuit 304 for directly connecting with the corresponding disk drivesamong the disk drives 14 a–14 d, as well as network connection circuits303 a and 303 b for connecting with the network switches 12 a and 12 b.All of these elements are connected to the processor 301 via a processorbus 305, which is a high-speed signal line bus.

In FIG. 3, the processing in the disk adapters 13 a–13 d is assumed tobe performed by having the corresponding processor 301 execute thecontrol programs stored in the corresponding local memory 302; however,as with the input/output channels 10 a–10 d, a part or all of thefunctions of the control program can alternatively implemented byhardware.

<Cache Memories>

FIG. 4 is an example of the configuration of the cache memories 11 a–11d. Each of the cache memories 11 a–11 d has a search control section 40and a memory section 41, where each data is stored in the memory section41 as a set of a significant bit V 401, a rewriting bit D 402, a datablock number 403 and a data content 404.

Each of the input/output channels 10 a–10 d can notify via an addressbus 411 the data block number 403 requested by a host computer andcauses the search control section 40 to search whether there is datawhose data block number 403 matches and whose significant bit V 401 isin a valid state (for example, “1”) in the memory section 41.

If the data is found as a result of searching, a hit signal is sent viaa response signal bus 412, and the fact that the matching data has beenfound is reported. In addition, the corresponding data content 404 isread via a data path 413. When writing data, a write command signal isnotified via a control command bus 414, data transferred by the datapath 413 is written to the corresponding data content 404, and therewriting bit D 402 goes into a set state (for example, “1”) to recordthat a rewrite has occurred. If no matching data is found as a result ofsearching, a miss signal is sent via the response signal bus 412, andthe fact that no matching data has been found is reported.

For example, if an invalidation signal for invalidating data in one ofthe cache memories 11 a–11 d is sent from one of the disk adapters 13a–13 d, the appropriate one of the input/output channels 10 a–10 dsimilarly notifies the corresponding data block number 403 via theaddress bus 411 and causes the search control section 40 to searchwhether there is data whose data block number 403 matches and whosesignificant bit V 401 is in a valid state (for example, “1”) in thememory section 41.

If the data is found as a result of searching, the content of thecorresponding rewriting bit D 402 is also checked. If the rewriting bitD 402 is in a set state, a dirty hit signal is sent via the responsesignal bus 412.

The appropriate one of the input/output channels 10 a–10 d that receivedthe dirty hit signal reads the corresponding data content 404 throughthe data path 413 and sends the data content 404 to the disk adapteramong the disk adapters 13 a–13 d that sent the invalidation signal. Ifthe rewriting bit D 402 is not in a set state, a clean hit signal issent via the response signal bus 412.

In both of these cases, the appropriate one among the input/outputchannels 10 a–10 d subsequently notifies the corresponding data blocknumber 403 via the address bus 411 and an invalidation command signalvia the control command bus 414, which sets the significant bit V 401 inan invalid state (for example, “0”) and invalidates the data set.

If the data is not found as a result of searching, a miss signal is sentvia the response signal bus 412, and the fact that the data was notfound is reported to the appropriate input/output channel among theinput/output channels 10 a–10 d. In all of these cases, the appropriateinput/output channel among the input/output channels 10 a–10 d at theend sends back an invalidation processing completion signal to the diskadapter among the disk adapters 13 a–13 d that sent the invalidationsignal, in order to communicate that the processing concerninginvalidation has been completed.

If the rewriting bit D 402 is in a set state and if it is recorded thatthe data read from one of the disk drives 14 a–14 d has been rewritten,the rewritten data is sent to the disk adapters 13 a–13 d after anappropriate amount of time has passed or when the cache memories 11 a–11d become full, in addition to when an invalidation takes place; afterdata is written back to the appropriate disk drive among the disk drives14 a–14 d, the rewriting bit D 402 is set to a reset state (for example,“0”), and the record that a rewriting has occurred is erased.

Although the search control section 40 actually performs a searchcontrol of the memory section 41 according to FIG. 4, only the memorysection 41 may be provided without the search control section 40, andthe processors 201 of the input/output channels 10 a–10 d can perform anequivalent function.

In addition, although there are various signal buses such as the addressbus 411, the response signal bus 412, the data path 413, and the controlcommand bus 414, and these are connected in a combined form to theinput/output channels 10 a–10 d according to FIG. 4, a single signal buscan be provided through which signal commands equivalent to the varioussignal buses, such as the address bus 411, the response signal bus 412,the data path 413 and the control command bus 414, are transferred onthe single signal bus.

According to the example in FIG. 4, data sets each comprising thesignificant bit V 401, the rewriting bit D 402, the data block number403 and the data content 404 are all stored in the single memory section41, such that when searching to determine whether matching data exists,the entire memory section 41 must be searched. As a result, it isconceivable for searching to become time-consuming as the capacity ofthe memory section 41 grows larger.

In such a case, the configuration as shown in FIG. 5 may be used. InFIG. 5, each of the cache memories 11 a–11 d comprises a control searchsection 50, a tag section 51 and a data section 52; in the tag section51 are stored a significant bit V 501, a rewriting bit D 502, a datablock number 503 and a data position in cache 504. In the data section52 is stored a data content 505.

In the tag section 51, contents equivalent to the corresponding contentsin FIG. 4 are recorded in the significant bit V 501, the rewriting bit D502 and the data block number 503. The position of data indicated in thedata section 52 is recorded in the data position in cache 504.

To take out a data content from the data section 52, the position of thedata is sent to the data section 52 via a data position signal 515 fromthe data position in cache 504 that corresponds to the data block number503, and the data content is read by a data path 513.

When writing data, data communicated via the data path 513 is written inthe position designated similarly by the data position signal 515.Signals sent by an address bus 511, a control command bus 513 or aresponse signal bus 512 are equivalent to the corresponding signals inFIG. 4.

By employing such a configuration, only the tag section 51 has to besearched when searching to determine whether certain data exists,according to the example in FIG. 5; consequently, even if the capacityof the data section 52 grows larger, the search time would not be veryaffected.

In other words, due to the fact that data contents are stored in thememory section 41 in the example in FIG. 4, numerous semiconductor chipsbecome necessary as the number of data blocks grows, which requiresnumerous semiconductor chips to be searched, which in turn requireslonger time for search.

In contrast, in the example in FIG. 5, semiconductor chips storing thedata section 52 that stores data contents and semiconductor chipsstoring the tag section 51 are separate; consequently, the number ofsemiconductor chips to store the tag section 51 can be few, whichrequires only few semiconductor chips to be searched, which in turnrequires shorter time for search.

Although the search control section 50 actually performs a searchcontrol of the tag section 51 according to FIG. 5, only the tag section51 and the data section 52 may be provided without the search controlsection 50, and the processors 201 of the input/output channels 10 a–10d can perform an equivalent function, as in the example in FIG. 4.

In addition, although there are various signal buses such as the addressbus 511, the response signal bus 512, the data path 513, and the controlcommand bus 514, and these are connected in a combined form to theinput/output channels 10 a–10 d according to FIG. 5, again as in theexample in FIG. 4, a single signal bus can be provided through whichsignal commands equivalent to the various signal buses, such as theaddress bus 511, the response signal bus 512, the data path 513 and thecontrol command bus 514, are transferred on the single signal bus.

<Data Table>

When data corresponding to a data block number requested from the hostcomputer is not found in the cache memories 11 a–11 d connected to oneof the input/output channels 10 a–10 d that received the request, a datatable, one of whose format examples is shown in FIG. 6, provided in eachof the input/output channels 10 a–10 d records to which of the diskadapters 13 a–13 d data should be requested.

A data block number and a disk adapter number are recorded as a set inthe data table in FIG. 6, where there are sets only in numberscorresponding to data block numbers predetermined between each of theinput/output channels 10 a–10 d and a host computer connected to each.

When storing a certain number (for example, 16) of consecutive datablock numbers in one of the disk drives 14 a–14 d connected to a singledisk adapter among the disk adapters 13 a–13 d, a set designated by adisk drive number and a disk adapter number of the first block numbercan be made to encompass all of the data blocks (for example, 16). Bydoing this, the size of the data table can be reduced to one-sixteenth,for example.

Such a data table is stored in the local memory 202 in FIG. 2, forexample, and read or written as necessary by the processor 201.

FIG. 7 is an example of the format of a data table that is stored in thedisk adapters 13 a–13 d, which records in which position of which diskdrive among the disk drives 14 a–14 d data corresponding to a data blocknumber requested from the input/output channels 10 a–10 d is stored.

A data block number, a disk drive number, a data position within adrive, and a send destination input/output channel number, whichindicates the input/output channel to which data is sent, are recordedas a set in the data table shown in FIG. 7. If data corresponding to acertain data block number has never been sent to any of the input/outputchannels 10 a–10 d, an invalid input/output channel number that ispredetermined is recorded as the corresponding send destinationinput/output channel number. Further, when the cache memory among thecache memories 11 a–11 d corresponding to the input/output channel amongthe input/output channels 10 a–10 d to which data was sent becomes full,causing the data to be turned away and deleted, an invalid input/outputchannel number can be set as the corresponding send destinationinput/output channel number.

In each of the disk adapters 13 a–13 d, there are entries provided inthe data table only in numbers corresponding to the data block numbersstored in one of the disk drives 14 a–14 d connected to each of thecorresponding disk adapters 13 a–13 d. The data table in reality isstored in the local memory 302 in FIG. 3, for example, and read orwritten as necessary by the processor 301.

<Command Format>

The following is a description of command formats for an invalidationcommand and an update command that are used in consistency maintainingprocessing for data stored in the cache memories 11 a–11 d.

When data sent to one of the input/output channels 10 a–10 d isrequested from another of the input/output channels 10 a–10 d, a commandformat for an invalidation command, one of whose examples is shown inFIG. 8, in the disk adapters 13 a–13 d is sent to the input/outputchannel to which the data was first sent to invalidate the data in thecorresponding cache memory among the cache memories 11 a–11 d. Theinvalidation command comprises an invalidation command code and a datablock number to be invalidated.

When rewriting of certain data in one of the input/output channels 10a–10 d occurs among a plurality of input/output channels 10 a–10 dhaving the same data, a command format for an update command, one ofwhose examples is shown in FIG. 9, is sent from the appropriate diskadapter among disk adapters 13 a–13 d to the appropriate input/outputchannel among the input/output channels 10 a–10 d in order to write backthe data to the appropriate disk drive among the disk drives 14 a–14 dthrough the corresponding disk adapter among the disk adapters 13 a–13d, and at the same time to rewrite and update the same pre-updated datain the cache memories 11 a–11 d corresponding to the other input/outputchannels 10 a–10 d, where the update command is sent instead of theinvalidation command in FIG. 8. The command format comprises, inaddition to a command code indicating an update command and a data blocknumber, update data for updating data content.

<Description of Processing>

The following is a detailed description of a processing that takes placein the disk array device 1 when a data input/output request, such as adata request or data write request, sent from a host computer isreceived.

FIG. 10 is one example of a data format of data input/output requestssent from a host computer to the disk array device 1. A header indicatesID of the host computer. A port ID indicates the port ID of the port towhich a logical volume, which is the subject of processing for the datainput/output request, is connected. Logical volumes refer to logicalstorage regions partitioned and established in storage regions of thedisk drives 14 a˜4 d. An LUN (Logical Unit Number) column indicates theidentifier of the logical volume that is the subject of the datainput/output request. An address column and a data length column areestablished when the data input/output request is a data request, forexample; in such a case, the address column indicates the beginningaddress of the logical volume that stores the read destination data,while the data length column indicates the length of data that is thesubject of reading.

A mode column indicates a value referred to in the disk array device 1to control the execution order of a response processing to the hostcomputer for the data input/output request and an consistencymaintaining processing for data in each of the cache memories 11 a–11 d.In this embodiment example, either “0” or “1” is set in the mode column.

A value “0” is set, for example, when high response speed to the hostcomputer is required rather than maintaining consistency of data storedin each of the cache memories 11 a–11 d in a data input/output requestprocessing. On the other hand, a value “1” is set, for example, whenconsistency of data stored in each of the cache memories 11 a–11 d mustbe maintained in a data input/output request processing.

<Data Request>

First, a processing that is performed in the disk array device 1 when adata request is received as a data input/output request sent from a hostcomputer is described below with reference to a flowchart in FIG. 11. Inthis example, it is the input/output channel 10 a that receives the datarequest, but the processing is similarly applicable when otherinput/output channels 10 b–10 d receive the data request.

Upon receiving a data request from a host computer (step 1110), theinput/output channel 10 a checks whether data that is the subject ofreading exists in the cache memory 11 a (step 1112). If it does exist(step 1112: YES), the input/output channel 10 a reads the data from thecache memory 11 a and sends it to the host computer (step 1113).

On the other hand, if the data requested does not exist in the cachememory 11 a (step 1112: NO), the input/output channel 10 a determinesbased on a data block number designated in the data request which amongthe disk adapters 13 a–13 d is connected to one of the disk drives 14a–14 d with the data, and sends the data request to the appropriate diskadapter among the disk adapters 13 a–13 d using one of the networkswitches 12 a and 12 b. Here, one of the disk drives that is connectedto the disk adapter 13 a is assumed to have the data. Upon receiving thedata request, the disk adapter 13 a determines which among the diskdrives 14 a and 14 b has the data based on the data block number (step1114), and begins to read the data from the disk drive (step 1115).

At this point, the disk adapter 13 a checks the content of a mode columnof the data request (step 1116); if “0” is set in the mode column (step1116: YES), after sending the data read from the disk drive to theinput/output channel 10 a (step 1117), the processing proceeds to step1118 and subsequent steps.

On the other hand, if “1” is set in the mode column (1116: NO), theprocessing proceeds directly to step 1118 and subsequent steps.

In step 1118, the disk adapter 13 a searches to determine whether thedata requested has previously been sent to any of the input/outputchannels 10 b–10 d other than the input/output channel 10 a.Specifically, this search takes place by searching whether a validinput/output channel number is registered under the send destinationinput/output channel number of the data table in FIG. 7 for the diskadapter 13 a.

If the data requested has never been sent from the disk adapter 13 a tothe cache memories 11 b–11 d corresponding to the other input/outputchannels 10 b–10 d (step 1119: NO), the processing proceeds to step1125. On the other hand, if the data requested has been sent previouslyfrom the disk adapter 13 a to the cache memories 11 b–11 d correspondingto the other input/output channels 10 b–10 d (step 1119: YES), aninvalidation command shown in FIG. 8 is sent to the input/output channelto which the data requested has been sent before (step 1120), and thedata is deleted from the cache memory corresponding to the input/outputchannel.

In addition, whether there has been any rewrite to the data in the cachememory corresponding to the input/output channel and whether therewritten data has not been written back to the appropriate disk driveare determined (step 1121). Specifically, these determinations are madeby examining the rewriting bit D 402 or 502 in FIG. 4 or 5,respectively. If the rewritten data has not been written back to theappropriate disk drive, the corresponding input/output channel readsfrom the cache memory the data that has not been written back and sendsthe data back to the appropriate disk adapter. The disk adapter, afterthe reading of data from the disk drive that began in step 1115 iscompleted, writes the rewritten data sent from the input/output channelover the data read from the disk drive (step 1122).

Next, the disk adapter waits for an invalidation processing completionsignal to be sent from the input/output channel to confirm that the datahas been invalidated (step 1123).

Next, by setting a predetermined invalid channel number in the senddestination input/output channel number of the data table in FIG. 7, therecord of the data send destination is deleted (step 1124). However,since a new input/output channel number of the input/output channel towhich data is sent will be recorded later (in step 1125), the processingin step 1124 may be omitted.

Next, the cache memory 11 a corresponding to the input/output channel 10a that received the data request in step 1110 is determined as thedestination for sending the data, and the input/output channel isrecorded accordingly (step 1125). Specifically, such a recording is doneby recording a valid channel number under the send destinationinput/output channel number of the data table in FIG. 7.

If reading from the disk drive that began in step 1115 has not yetcompleted, the disk adapter 13 a waits until the reading is completed;once the reading is completed, the data read is sent to the input/outputchannel 10 a and stored in the cache memory 11 a connected to theinput/output channel 10 a (step 1126).

Next, the disk adapter 13 a checks the content of the mode column of thedata request (step 1127); if “1” is set in the mode column (step 1127:YES), the disk adapter 13 a sends the data read from the disk drive tothe input/output channel 10 a (step 1128) and proceeds to step 1129 andsubsequent steps. On the other hand, if “0” is set in the mode column(step 1127: NO), the processing proceeds to step 1129 and subsequentsteps.

In step 1129, whether the data that has passed through step 1129 and wasread from the disk drive has been overwritten is determined. If it hasbeen overwritten, the overwritten data is written back to theappropriate disk drive (step 1130).

If “1” is set in the mode column in the processing above, i.e., aninvalidation processing is to be performed before responding to the hostcomputer, the processing speed can be enhanced by completing theprocessing to read data from the disk drive (step 1115) by the time ofcompletion of processing in step 1122 and step 1126, in other words, byoverlapping these processings.

As described above, in this embodiment example, if “0” is set in themode column in step 1116, the processing that begins in step 1118 isexecuted after the data read from a disk drive is first sent to the hostcomputer. In other words, if “0” is set in the mode column of the datainput/output request, the processing in steps 1118 through 1130 that isrequired to maintain consistency of data stored in each of the cachememories 11 a–11 d takes place after the response processing to the hostcomputer from the disk array device 1 takes place, which enhances theresponse speed to the host computer.

As a result, if consistency does not have to be maintained due to thespecification or nature of software operating on the host computer, oreven if it does, it does not have to be strictly maintained, theresponse speed to the host computer can be enhanced for such a datainput/output request by setting “0” in the mode column of the datainput/output request from such software.

The processing for invalidation such as in step 1120 may be a factorthat reduces the response speed in responding to the host computer,since communications for requesting invalidation or for checking thatinvalidation has taken place are done by a switch. However, by havingthe invalidation process takes place after-the-fact, i.e., after theresponse processing to the host computer, the response speed to the hostcomputer can be improved.

In FIG. 11, a processing to determine that “0” is set as the mode and asend processing to the host computer (steps 1116 and 1117) take placebefore step 1118; however, these processing can alternatively take placebetween step 1118 and step 1119 or between step 1119 and step 1120, forexample. In other words, as long as the structure allows the response tothe host computer to take place before those consistency maintainingprocessing that are the main factors for reducing the response speed tothe host computer among processing required to maintain consistency ofdata stored in each of the cache memories 11 a–11 d, an enhancement inthe response speed to the host computer can be expected.

[Data Write Request]

The following is a processing that is performed in the disk array device1 when a data write request is received as a data input/output requestsent from a host computer. In this example, it is the input/outputchannel 10 a that receives the data write request, but the processing issimilarly applicable when other input/output channels 10 b–10 d receivethe data write request.

A flowchart in FIG. 12 describes an embodiment example of a processingthat takes place in a disk array device 1 when data that has been sentto one of the input/output channels 10 a–10 d is requested by otherinput/output channels 10 a–10 d to be sent and the appropriate diskadapter among the disk adapters 13 a–13 d sends to the firstinput/output channel among the input/output channels 10 a–10 d aninvalidation signal to invalidate the data that is in one of the cachememories 11 a–11 d that corresponds to the first input/output channelamong the input/output channels 10 a–10 d in order to maintainconsistency of data in each of the cache memories 11 a–11 d, where thepresent processing controls the execution order of an consistencymaintaining processing and a processing to notify completion to the hostcomputer according to the mode of the content of the data input/outputrequest.

Upon receiving a data write request from a host computer (step 1211),the input/output channel 10 a checks the content of the mode column ofthe data write request (1212). If “0” is set in the mode column (step1212: YES), the input/output channel 10 a permits writing to the cachememory 11 a corresponding to the input/output channel 10 a and the datato be written is written in the cache memory 11 a (step 1213); and theinput/output channel 10 a sends a write completion notice to the hostcomputer (step 1214). On the other hand, if in step 1212, “1” is foundto be set in the mode column (step 1212: NO), instead of writing thedata in the cache memory 11 a immediately, the input/output channel 10 aproceeds to step 1215.

Next, the input/output channel 10 a notifies the appropriate diskadapter among the disk adapters 13 a–13 d of the fact that the datawrite request has been made; the disk adapter upon being notifiedsearches whether there are cache memories 11 b–11 d corresponding to anyof the input/output channels 10 b–10 d that sent the data other than theinput/output channel 10 a that received the data write request (step1215). If there are no other cache memories 11 b–11 d corresponding toany of the input/output channels 10 b–10 d that sent the data (step1216: NO), the processing proceeds to step 1220. On the other hand, ifthere are cache memories 11 b–11 d corresponding to any of theinput/output channels 10 b–10 d that sent the data, an invalidationrequest is sent to every applicable input/output channel among theinput/output channels 10 b–10 d with their corresponding cache memories11 b˜11 d as the subject of the invalidation request (step 1217). Forthe invalidation request, the invalidation command shown in FIG. 8, forexample, can be used.

Once it is confirmed that invalidation has taken place (step 1218), theinput/output channel numbers of the cache memories among the cachememories 11 b–11 d that have been invalidated are deleted from recordunder the send destination input/output channel number (step 1219).

Next, in step 1220, the content of the mode column of the data writerequest is checked. If “1” is set in the mode column, the processingproceeds to step 1221, where writing data to the cache memory 11 acorresponding to the input/output channel 10 a that received the datawrite request is permitted and write data is received from the hostcomputer and written to the cache memory 11 a (step 1221), and a writecompletion notice is sent to the host computer (step 1222). The datawritten to the cache memory 11 a is sent from the input/output channel10 a to the appropriate disk adapter among the disk adapters 13 a–13 d,and data is written back to the appropriate disk drive among the diskdrives 14 a–14 d (step 1223).

On the other hand, if in step 1220, “0” is found to be set in the modecolumn, the processing proceeds to step 1223, since the processing thatis equivalent to the processing in step 1221 has already taken place instep 1213.

As described above, when “0” is set in the mode column, the disk arraydevice 1 according to the present embodiment example executes aprocessing for consistency maintenance after first sending the data readfrom one of the disk drives 14 a–14 d to the host computer. In otherwords, when “0” is set in the mode column of the data input/outputrequest, the processing for consistency maintenance takes placeafter-the-fact, i.e., after a response processing from the disk arraydevice 1 to the host computer has taken place, which enhances theresponse speed to the host computer.

As a result, if consistency does not have to be maintained due to thespecification or nature of software operating on the host computer, oreven if it does, it does not have to be strictly maintained, theresponse speed to the host computer can be enhanced for such a datainput/output request by setting “0” in the mode column of the datainput/output request from such software.

A flowchart in FIG. 13 describes an embodiment example of a processingby the disk array device 1, which takes place when a data rewrite occursin one of the cache memories 11 a–11 d that corresponds to one of theinput/output channels 10 a–10 d and the rewritten data is written backto the appropriate disk drive among the disk drives 14 a–14 d throughthe appropriate disk adapter among the disk adapters 13 a–13 d, and atthe same time the same pre-rewritten data in other cache memories 11a–11 d that corresponds to other input/output channels 10 a–10 d isrewritten and updated, in order to maintain consistency of data in eachof the cache memories 11 a–11 d, wherein the present processing controlsthe execution order of a consistency maintaining processing and aprocessing to notify completion to the host computer according to themode of the content of the data input/output request.

Upon receiving a data write request from a host computer (step 1311),the input/output channel 10 a permits writing of data to the cachememory 11 a corresponding to the input/output channel 10 a and writesthe data to the cache memory 11 a (step 1312).

Next, the content of the mode column of the data write request ischecked (step 1313); if “0” is set in the mode column (step 1313: YES),the input/output channel 10 a sends a write completion notice to thehost computer (step 1314). On the other hand, if in step 1313 “1” isfound to be set in the mode column (step 1313: NO), the processingproceeds to step 1315.

In step 1315, the write data is sent to the appropriate disk adapteramong the disk adapters 13 a–13 d from the input/output channel 10 a atappropriate timing, and the data written to the cache memory 11 a isalso written back to the original disk drive among the disk drives 14a–14 d (step 1315).

Next, the appropriate disk adapter among the disk adapters 13 a–13 dchecks whether there are cache memories 11 b–11 d that correspond to anyof the input/output channels 10 b–10 d that sent the data previously,other than the input/output channel 10 a in which data writing occurred(step 1316). If there are cache memories 11 b–11 d that correspond toany of the input/output channels 10 b–10 d that have sent the datapreviously (step 1317: YES), the processing proceeds to step 1318. Ifthere are no such cache memories 11 b–11 d, the processing proceeds tostep 1319.

In step 1318, the write data that has been written to the appropriatedisk drive by the appropriate disk adapter is sent to every cache memoryamong the cache memories 11 b–11 d corresponding to any of theinput/output channels 10 b˜10 d that have the data, and the old data isoverwritten by the new.

In 1319, the value in the mode column of the data write request ischecked; if “1” is set in the mode column (step 1319: YES), a writecompletion notice is sent to the host computer (step 1320). On the otherhand, if “0” is set in the mode column (step 1320: NO), the completionnotice is not sent since it has already been sent in 1314.

As described above, according to the present embodiment example, when“0” is set in the mode column, the processing for consistencymaintenance is executed after the data read from the disk drives 14 a–14d is first sent to the host computer. In other words, if “0” is set inthe mode column, the processing for consistency maintenance takes placeafter the response processing to the host computer from the disk arraydevice 1, such that the response to the host computer takes place beforethe processing for consistency maintenance, which enhances the responsespeed to the host computer.

As a result, if consistency does not have to be maintained due to thespecification or nature of software operating on the host computer, oreven if it does, it does not have to be strictly maintained, theresponse speed to the host computer can be enhanced by setting “0” inthe mode column of such a data input/output request from such software.

<Other Embodiments>

In the preceding embodiment examples, the execution order of a responseprocessing to the host computer regarding a data input/output requestand an consistency maintaining processing for data in each of the cachememories 11 a–11 d is controlled according to the value in the modecolumn of the data input/output request. However, the execution order ofthe two processing can be switched based on the value of LUN describedin the data input/output request instead of the value in the modecolumn.

Specifically, in parts of the flowcharts in FIGS. 11 through 13 wherethe execution control takes place based on the value in the mode column,the value of LUN would be referred to instead of the value in the modecolumn and the processing would branch off based on the value of LUN.How the execution order can be controlled based on the value set in themode column or the LUN value can, for example, be set by an operatoroperating a management terminal of the disk array device 1.

Some new disk array devices have a function to store, depending on thedata input/output request, contents of data managed in its own logicalvolumes additionally on other disk array devices that are installed inremote location and connected to the disk array devices (where thefunction is sometimes called a “remote copying function”) for thepurpose of enhancing availability or disaster recovery performance.

As a method to realize such a function, other disk array devices can becommunicatively connected to the input/output channels provided on thedisk array device 1, and operation modes can be made switchable from ahost computer through commands sent from the host computer to the diskarray device 1 to switch between an operation mode in which theinput/output channels write data to the disk array device's own diskdrives (hereinafter called a “normal mode”) and an operation mode inwhich the input/output channels send data input/output requests to theother disk array devices (hereinafter called a “copy mode”).

If such a function is realized through such a method, the executionorder of a processing to respond to a host computer for a datainput/output request and a consistency maintaining processing for datain each cache memory can be controlled depending on which operation modethe input/output channel that received the data input/output request isoperating in. In other words, for a data input/output request receivedby an input/output channel operating in the copy mode, for example, thepriority is placed on the response to the host computer and theprocessing for consistency maintenance is performed later; on the otherhand, for a data input/output request received by an input/outputchannel operating in the normal mode, the priority is placed on theprocessing for consistency maintenance and the response to the hostcomputer takes place subsequently.

In other words, processing for data input/output requests received byinput/output channels operating in the copy mode is deemed to often haveless need for consistency maintenance compared to processing for datainput/output requests received by input/output channels operating in thenormal mode; consequently, the response speed to the host computer canbe enhanced in the copy mode by applying the mechanism described.

This concludes the description of a disk array device according to thepresent invention, but the embodiments of the present invention serveonly to facilitate the understanding of the present invention and do notlimit the present invention. Many modifications can be made withoutdeparting from the present invention.

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof. The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention.

The presently disclosed embodiments are therefore to be considered inall respects as illustrative and not restrictive, the scope of theinvention being indicated by the appended claims, rather than theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

1. A disk array device comprising: a plurality of input/output channels that receive data input/output requests from at least one external device; a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels; a disk drive device; a disk control module that performs data input/output to and from the disk drive device; at least one communication module that communicatively connects the input/output channels with the disk control module; and a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of a consistency maintaining processing to maintain consistency of data stored in each of the cache memories such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary.
 2. A disk array device according to claim 1, further comprising: a consistency maintaining module that performs the consistency maintaining processing to maintain consistency of data stored in each of the cache memories.
 3. A disk array device according to claim 1, wherein, when data stored in one of the cache memories is updated, the consistency maintaining module invalidates data stored in at least another one of the cache memories.
 4. A disk array device according to claim 1, wherein, when data stored in one of the cache memories is updated a consistency maintaining module updates data stored in at least another one of the cache memories.
 5. A disk array device comprising: a plurality of input/output channels that receive data input/output requests from at least one external device; a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels; a disk drive device; a disk control module that performs data input/output to and from the disk drive device; at least one communication module that communicatively connects the input/output channels with the disk control module; and a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of a consistency maintaining processing to maintain consistency of data stored in each of the cache memories such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein a consistency maintaining module performs the consistency maintaining processing to maintain consistency of data stored in each of the cache memories, and wherein the consistency maintaining module performs the consistency maintaining processing depending on a content of the data input/output request.
 6. A disk array device according to claim 5, wherein the consistency maintaining module performs the consistency maintaining processing first depending on a content of the data input/output request, and then a response processing to the external device is executed.
 7. A disk array device comprising: a plurality of input/output channels that receive data input/output requests from at least one external device; a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels; a disk drive device; a disk control module that performs data input/output to and from the disk drive device; at least one communication module that communicatively connects the input/output channels with the disk control module; and a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of a consistency maintaining processing to maintain consistency of data stored in each of the cache memories such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein, when data stored in one of the cache memories is updated, a consistency maintaining module invalidates data stored in at least another one of the cache memories, wherein the data stored in the one of the cache memories and the data stored in the at least another one of the cache memories are stored in an identical storage region of the disk drive device, and wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary.
 8. A disk array device comprising: a plurality of input/output channels that receive data input/output requests from at least one external device; a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels; a disk drive device; a disk control module that performs data input/output to and from the disk drive device; at least one communication module that communicatively connects the input/output channels with the disk control module; and a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of a consistency maintaining processing to maintain consistency of data stored in each of the cache memories such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein the data stored in the one of the cache memories and the data stored in the at least another one of the cache memories are stored in an identical storage region of the disk drive device, and wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary.
 9. A disk array device comprising: a plurality of input/output channels that receive data input/output requests from at least one external device; a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels; a disk drive device; a disk control module that performs data input/output to and from the disk drive device; a communication module that communicatively connects the input/output channels with the disk control module; a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories; and a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and operations is executed second, wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary.
 10. A disk array device according to claim 9, wherein, when data stored in one of the cache memories is updated, the consistency maintaining module invalidates data stored in at least another one of the cache memories.
 11. A disk array device according to claim 9, wherein, when data stored in one of the cache memories is to be updated, the data stored in the one of the cache memories is updated and data stored in at least another one of the cache memories is also updated.
 12. A disk array device comprising: a plurality of input/output channels that receive data input/output requests from at least one external device; a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels; a disk drive device; a disk control module that performs data input/output to and from the disk drive device; a communication module that communicatively connects the input/output channels with the disk control module; a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories; and a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein, when data stored in one of the cache memories is updated, the consistency maintaining module invalidates data stored in at least another one of the cache memories, wherein the data stored in the one of the cache memories and the data stored in the at least another one of the cache memories are stored in an identical storage region of the disk drive device, and wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary.
 13. A disk array device comprising: a plurality of input/output channels that receive data input/output requests from at least one external device; a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels; a disk drive device; a disk control module that performs data input/output to and from the disk drive device; a communication module that communicatively connects the input/output channels with the disk control module; a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories; and a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein, when data stored in one of the cache memories is to be updated, the data stored in the one of the cache memories is updated and data stored in at least another one of the cache memories is also updated, wherein the data stored in the one of the cache memories and the data stored in the at least another one of the cache memories are stored in an identical storage region of the disk drive device, and wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary.
 14. A disk array device comprising: a plurality of input/output channels that receive data input/output requests from at least one external device; a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels; a disk drive device; a disk control module that performs data input/output to and from the disk drive device; a communication module that communicatively connects the input/output channels with the disk control module; a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories; and a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and operations is executed second, wherein a plurality of logical volumes of logical storage regions is set on a storage region of the disk drive device, the data input/output request includes an identifier for identifying at least one of the logical volumes that is a subject of the data input/output request, and further comprising a module that performs the control of the execution order according to the identifier included in the data input/output request.
 15. A disk array device comprising: a plurality of input/output channels that receive data input/output reguests from at least one external device; a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels; a disk drive device; a disk control module that performs data input/output to and from the disk drive device; a communication module that communicatively connects the input/output channels with the disk control module; a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories; a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and operations is executed second; a module that connects to another disk array device; and a module that, upon receiving a data write request as the data input/output request, writes data designated by the data write request in the disk drive device, and sends a write request for the data to the other disk array device.
 16. A disk array device according to claim 15, wherein each of the input/output channels, upon receiving a data write request, operates in one of a write operation mode to write data in the disk drive device and a request send operation mode to send the write request to the other disk array, and further comprising a module that performs the control of the execution order depending on which one of the write operation mode and the request send operation mode one of the input/output channels that receives the data input/output request is operating in.
 17. A method for controlling a disk array device, the disk array device comprising a plurality of input/output channels that receive data input/output requests from at least one external device, a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels, a disk drive device, a disk control module that performs data input/output to and from the disk drive device, a communication module that communicatively connects the input/output channels with the disk control module, and a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories, the controlling method comprising the steps of: receiving a data input/output request from the at least one external device; and controlling a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary.
 18. A method for controlling a disk array device, the disk array device comprising a plurality of input/output channels that receive data input/output requests from at least one external device, a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels, a disk drive device, a disk control module that performs data input/output to and from the disk drive device, a communication module that communicatively connects the input/output channels with the disk control module, and a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories, the controlling method comprising the steps of: receiving a data input/output request from the at least one external device; and controlling an execution order of a response processing to respond to the at least one external device according to the data input/output request and the consistency maintaining processing, wherein the consistency maintaining processing includes the step of, upon updating data stored in one of the cache memories, invalidating data stored in at least another one of the cache memories wherein the data stored in the at least another one of the cache memories is stored in an identical storage region of the disk drive device that stores the data stored in the one of the cache memory, and wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary.
 19. A method for controlling a disk array device, the disk array device comprising a plurality of input/output channels that receive data input/output requests from at least one external device, a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels, a disk drive device, a disk control module that performs data input/output to and from the disk drive device, a communication module that communicatively connects the input/output channels with the disk control module, and a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories, the controlling method comprising the steps of: receiving a data input/output request from the at least one external device; and controlling a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein the consistency maintaining processing includes the step of, upon updating data stored in one of the cache memories, updating data stored in at least another one of the cache memories wherein the data stored in the at least another one of the cache memories is stored in an identical storage region of the disk drive device that stores the data stored in the one of the cache memory, and wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary.
 20. A method for controlling a disk array device, the disk array device comprising a plurality of input/output channels that receive data input/output requests from at least one external device, a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels, a disk drive device, a disk control module that performs data input/output to and from the disk drive device, a communication module that communicatively connects the input/output channels with the disk control module, and a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories, the controlling method comprising the steps of: receiving a data input/output request from the at least one external device; and controlling a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein a plurality of logical volumes of logical storage regions is set on a storage region of the disk drive device, the data input/output request includes an identifier for identifying at least one of the logical volumes that is a subject of the data input/output request, and the control of the execution order is conducted according to the identifier included in the data input/output request.
 21. A method for controlling a disk array device, the disk array device comprising a plurality of input/output channels that receive data input/output requests from at least one external device, a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels, a disk drive device, a disk control module that performs data input/output to and from the disk drive device, a communication module that communicatively connects the input/output channels with the disk control module, and a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories, the controlling method comprising the steps of: receiving a data input/output request from the at least one external device; and controlling a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein the disk array device connects to another disk array device, and further comprising the steps of upon receiving a data write request as the data input/output request, writing data designated by the data write request in the disk drive device, and sending a write request for the data to the other disk array device.
 22. A method for controlling a disk array device according to claim 21, wherein each of the input/output channels, upon receiving a data write request, operates in one of a write operation mode to write data in the disk drive device and a request send operation mode to send the write request to the other disk array, and the control of the execution order is conducted depending on which one of the write operation mode and the request send operation mode one of the input/output channels that receives the data input/output request is operating in.
 23. A storage system comprising: at least one external device; and a disk array device including a plurality of input/output channels that receive data input/output requests from at least one external device, a plurality of cache memories provided for the corresponding respective input/output channels, each of the cache memories connected to each of the corresponding respective input/output channels, a disk drive device, a disk control module that performs data input/output to and from the disk drive device, a communication module that communicatively connects the input/output channels with the disk control module, and a consistency maintaining module that performs a consistency maintaining processing to maintain consistency of data stored in each of the cache memories, wherein the disk array device includes a control module that controls, upon receiving a data input/output request from the at least one external device, a sequence of execution of a first operation of a response processing to respond to the at least one external device according to the data input/output request and a second operation of the consistency maintaining processing such that one of said first and second operations is executed first and the other of said first and second operations is executed second, wherein an analysis of the data input/output request is performed to determine whether maintaining consistency of data stored in each cache memory is necessary and the sequence of execution is controlled so that said first operation is executed first if maintaining consistency is not necessary. 